The invention relates to an exhaust-gas recycling device for an internal-combustion engine, with an exhaust-gas recycling line branched off from an exhaust-gas line to an inlet line and with an exhaust-gas recycling valve arranged in the exhaust-gas recycling line and comprising a valve controlling the connection between the inlet and outlet lines and a pneumatic control drive consisting of two diaphragms which are clamped in a housing and which are connected operatively to a closing part of the valve, at least one diaphragm being connected firmly to the closing part, and the two diaphragms each being loaded by a spring in the closing direction of the closing part, the diaphragms subdividing the housing into at least two control chambers, of which a first control chamber located between the diaphragms can be subjected to a control pressure determined as a function of the engine running and a second control chamber formed by the second diaphragm and the housing can be subjected to a further control pressure.
An exhaust-gas recycling device of this type is known, for example, from German Patent Specification 2,528,760. There, the exhaust-gas recycling valve is controlled simultaneously as a function of the throughput of combustion gas and of the engine load state. The load state is detected from the height of the vacuum within the fresh-gas intake line, and the gas throughput is detected from the height of the exhaust-gas counterpressure in the exhaust-gas line. The gradient between the two pressures determines the particular opening cross-section of the exhaust-gas recycling valve. The actuating drive for the closing part of the exhaust-gas recycling valve consists of diaphragms connected to this and exposed to the above-mentioned pressure gradient.
Such a control of the exhaust-gas recycling valve is incapable of eliminating disturbing influences arising from unintentional changes of flow resistance in the fresh-gas intake and/or exhaust-gas line. Such changes of flow resistance can occur, for example, because filters in the intake line and/or exhaust-gas line become clogged. An especially disturbing effect is caused, in that respect, by so-called soot burn-off filters in diesel engines when the soot is burnt off intermittently on these. For then, the throughflow resistance of the filter varies undesirably over a wide range during the running of the engine, with the result that the exhaust-gas recycling quantity dependent on the pressure gradient between the intake and exhaust-gas lines for a specific opening cross-section of the exhaust-gas recycling valve is falsified in relation to the value which it should actually have on the basis of the predetermined control of the exhaust-gas recycling valve as a function of the engine running.
An object of the invention is to provide an improvement in such an exhaust-gas recycling device.
This object is achieved according to the invention by providing an arrangement wherein the second control chamber is subjected as a control pressure to the exhaust-gas pressure from the exhaust-gas line.
An embodiment which is highly advantageous in terms of construction includes an arrangement wherein, interposed between the first and second control chambers is a third control chamber which is separated from the first control chamber by a rigid connecting wall and on which the compression spring of the second diaphragm is supported, wherein the second diaphragm is attached rigidly to the first diaphragm via a driving rod guided displaceably through the connecting wall, wherein a third diaphragm sealing off the lead-in of the driving rod through the connecting wall is arranged in the third control chamber, and wherein the third control chamber is subjected to a control pressure from the inlet line.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.